In a medical imaging system, such as a computer tomography (CT) and ultrasound, a diagnostic image of a human tissue is usually obtained utilizing a contrast enhancement technique. Taking a CT imaging technique as an example, contrast media is injected into a human blood vessel before scanning, so as to reach to the tissue of interest, e.g., heart, liver and the like, which needs to be diagnosed, along with the blood flow, such that a degree of absorption of the blood vessel for X-rays is obviously different from the other tissues around it, whereby a diagnostic image having an enhanced contrast may be obtained in scanning
Usually, scanning is delayed for a period of time after the contrast media is injected, which can obtain a better scanning image. Such delayed time is generally a time from injection of the contrast media to its CT value reaching a peak value. Therefore, for different body tissues, acquisition of an accurate delay time is a key to affect the image quality and even a diagnostic result.
In the prior art, an operator generally injects a little contrast media, and during the process that the contrast media is injected and then enhanced, a pre-scan is performed at a certain time frequency to obtain a plurality of CT images, then regions of interest are drawn in each image manually. By recording CT values of the pixels of the region of interest at a plurality of disperse time points, a curve of CT values in function of time, i.e., HU-Time curve is drawn manually. And by observing the peak value of the curve, it may be determined that the time from injection of the contrast media to the CT value of the region of interest reaching to the peak value is the delay time of the pre-scan, and then a scan delay time in diagnosing may be calculated by a proper formula transformation based on the composition, dosage and the like of the contrast media. In a formal imaging scan diagnose, it may be determined as to when the region of interest is performed a CT scan based on the scan delay time in diagnosing.
The prior art utilizes such a method of manually determining a region of interest, which has a complicated operation and a high time cost, and due to the reasons such as beam hardening artifact, motion artifact and even irregular shape of the region of interest, it is very easy to mark the region of interest in a wrong place. Thus, the obtained HU-Time curve is not accurate enough, and the obtained scan delay time is not accurate, either.
Therefore, there is a need to provide a novel apparatus and method of medical imaging, which can avoid complicated manual operation, reduce the time cost and obtain the region of interest accurately in scanning image, consequently obtaining a more accurate HU-Time curve and a more accurate scan delay time, thus improving the quality of the scanned diagnostic image.